1. Field of the Invention
This invention pertains to pipe feeding systems of the type used to deliver single forty-foot lengths of pipe or multiple, welded together forty-foot lengths of pipe to the pipeline moving path, called the "firing line," aboard a pipeline laying vessel.
2. Description of the Prior Art
Various systems have been used on decks heretofore for transporting pipe or multiple, welded together lengths of pipe from a pipe supply conveyor, usually positioned along the outside of the deck, and the completed pipeline, which generally moves in a fore and aft path along the center of the deck. A difficulty in handling this pipe is caused by the fact that the diameter of vessel laid pipeline is getting increasingly larger, for example, in some cases up to 72 inches, and requires higher strength apparatus for carrying the loads. The difficulty is aggravated when the pipe laying vessel is rolling in heavy seas, and thus the heavy cylindrical pipe is subjected to forces trying to make them roll. The cost of operating a pipeline laying vessel amounts to many thousands of dollars per day. It thus becomes extremely important that the equipment handling the pipe be capable of withstanding both the forces acting on the pipe and the corrosive marine environment so that downtime for maintenance or repair is minimized.
None of the prior art devices meets all of these requirements satisfactorily. One prior art device employs a set of roller chains for carrying multiple sections of pipe from a pipe supply conveyor to the firing line. At each end of the conveyor, an accessory feeding device is required to transport the pipe from the supply conveyor to the chains and thence from the chains to the firing line. Still another device uses a walking beam in which a movable beam having a plurality of pipe holding saddles is lifted and then pivoted, carrying the pipe toward the firing line. The beam is then lowered, resting the pipe on a stationary set of supports while it pivots back a distance equal to one saddle and repeats the process. Both of these prior art systems are expensive to build and maintain and are subject to frequent breakdown due to the stresses on the devices.
Another prior art type of feeding mechanism is a reciprocable mobile cart having a single saddle. The cart rides on rails alongside a stationary set of pipe supports, each having a plurality of saddles. This type of cart is very time-consuming to operate since it must pick up a pipe at the supply conveyor and move it to the first saddle on the stationary supports. It must then go to the end of the stationary supports and unload a pipe into the firing line. Then it must come back to the stationary supports and, through short reciprocating movements, individually lift each pipe and advance it one saddle along the stationary supports. This is particularly time-consuming when the temporary lack of pipe from the supply causes a "void" or empty saddle in the feeding mechanism, which results in additional trips by the cart to catch up or fill all of the saddles to assure a constant supply of pipe to the pipeline moving path.